A lacking of understanding about cooling effects on methane (CH4) fluxes and potential asymmetrical responses to warming and cooling causes uncertainty about climate change effects on the atmospheric CH4 concentration. We investigated CH4 fluxes in an alpine meadow on the Tibetan Plateau in response to climate warming and cooling.
A 2-year reciprocal translocation experiment was implemented to simulate climate warming (i.e. downward translocation) and cooling (i.e. upward translocation) along an elevation gradient with four different vegetation types (at 3200, 3400, 3600 and 3800 m elevation) during the growing season (May to October) in 2008 and 2009.
Although the effects of warming and cooling varied depending on vegetation type, elevation and timescale (i.e., daily and seasonally), warming increased average seasonal CH4 uptake by 60 %, while cooling reduced it by 19 % across all vegetation types, based on a 1.3-5.1 A degrees C difference in soil temperature at 20 cm depth. Soil temperature over the range of 4-10 A degrees C explained 11-25 % of the variation in average seasonal CH4 fluxes, while there was no relationship with soil moisture over the range of 13-39 % and soil NH4 (+)-N and NO3 N- content. Methane uptake was more sensitive to warming than to cooling.
Because of warming and cooling spells in the alpine region, warming effects on CH4 uptake would be over-estimated by 64 % if cooling effects on it are not considered. Our findings suggest that asymmetrical responses of CH4 fluxes to warming and cooling should be taken into account when evaluating the effects of climate change on CH4 uptake in the alpine meadow on the Tibetan plateau.